Process for coating an object with a bright nickel/chromium coatin

ABSTRACT

Objects are coated with a basic bright nickel layer, an intermediate layer in which solid particles are embedded, and a chromium layer. The solid particles comprise particles of a solid, nonacid-resistant silicate which gives an alkaline reaction in aqueous suspension. The resulting composite coating has an outstanding corrosion resistance.

United States Patent Odekerken 1 Feb. 22, 1972 [54] PROCESS FOR COATING AN OBJECT [56] References Cited WITH A BRIGHT NICKEL/CHROMIUM COATING UNITED STATES PATENTS 1,574,363 2/ 1926 Calvert ..252/53.7 [721 lnvenm Mes Mane 'odekerken, W81, Nether- 2,590,566 3/1952 Osborn ..23/110 lands 3,033,648 5/1962 Vander Linden..... ....23/110 73 Assignee: NA]. Research Holland ispneflngenbosch, 3,115,391 12/1963 Lemeweben ..23/ 110 Netherlands 3,152,971 10/1964 Tomaszewski et al.... .....204/41 3,152,972 10/1964 Brown et a1 ..204/41 [22] Filed: F 19, 968 3,268,307 8/1966 Tomaszewski et a1. .....204/40 X [21] APPLNO: 706,619 3,268,424 8/1966 Brown etal ..204/4l Related us. Appficafion Data FOREIGN PATENTS OR APPLICATIONS [63] Continuatiomimpan of Ser No 336,015 Jan; 6, 287,612 2/1965 Netherlands ..204/4l 1964 abandoned Primary Examiner-G. L. Kaplan [301 Foreign Application Prior), Data Attorney--Tashof and Osheroff Jan. 9, 1963 Netherlands ..287612 1 1 ABSTRACT Objects are coated with a basic bright nickel layer, an inter- [52] U.S.Cl ..204/38 B, 29/ 183.5, 29/195, mediate layer in which Solid particles are embedded and a 29/196'6 7/71 117/130 204/16 204/40 chromium layer. The solid particles comprise particles of a 204/41 204/49 204/ solid, nonacid-resistant silicate which gives an alkaline reac- [51] int. Cl. ..C23b 5/50, C23C 3/02 tie in aqueous Suspension The resulting composite coating [58] Field of Search ..204/38, 38.2, 41, 40, 49, 181; has an outstanding corrosion resistance 10 Claims, No Drawings PROCESS FOR COATING AN OBJECT WITH-ABRIGHT NICKEL/CHROMIUM COATING CROSS-REFERENCES TO RELATED APPLICATIONS This application is a continuation-in-part of my copending 5 BACKGROUND OF THE INVENTION AND DESCRIPTION OF THE PRIOR ART It is known to apply a nickel coating to an object from a bath in which are dispersedone or more finely divided solids which are insoluble in the bath, such as silicates, for'example, of aluminum, magnesium, boron, calcium, strontium, and/or barium, such as kaolin, glass powder, tallow, mica, celsian, and the like, having a particle size below 5 microns. The resulting nickel coating has a satiny appearance, so that a chromium-layer plated over the nickel coating does not have the brightness required for the majority of uses for nickel/chromium coatings. However, such satiny coatings have a great corrosion resistance, which may be attributed to the fact that during the application of the chromium layer no chromium is deposited on the locations where solid particles which are electric nonconductors or poor conductors are present on the surface of the satiny nickel layer, so that a microporous chromium layer is formed. Owing to the presence of numerous micropores in the chromium layer, the greatest possible surface area of the subjacent nickel layer is exposed, so that the corrosion current caused by element action per unit of surface area is minimal.

ln my'U.S. patent application Ser. No. 260,854, now U.S. Pat. No. 3,298,802, there is described a method of coatingan object with a bright nickel/chromium coating comprising providingan object having thereon a bright nickel plating, applying thereto an intermediate metal layer containing particles, said particles having a conductivity not exceeding the conductivity of graphite, and plating chromium over said intermediate layer. The thickness of said intermediate layer preferably does not exceed a thickness of the order of about a few microns.

There is thus obtained a bright nickel/chromium coating having a high corrosion resistance. The coating owes its high corrosion resistance to the microporous structure of the chromium layer, which is caused by the electrically nonconductive or poorly conductive solid particles originating-from the solid material suspended in the bath fromwhich the intermediate layer is deposited, andwhich are embedded in said intermediate layer. The nickel/chromium coating owes its brightness to the fact that the thickness of the intermediate layer containing embedded solid particles is so minute that the brightness of the basic nickel layer is practically not diminished by the intermediate layer.

SUMMARY OF THE INVENTION It has now been found that the corrosion resistance of the nickel/chromium coating obtained by the process just prescribed is considerably improved by the incorporation in the bath from which the intermediate layer is deposited of a suspension of non-acid-resistant silicates which give an alkaline reaction in water.

The present invention accordingly provides, in a process for coating an object with a bright nickel/chromium coating, comprising the steps of providing an object having thereon a bright nickel coating, applying to said coating an intermediate metal layer containing particles from a plating bath containing said particles in suspension, and plating chromium over said intermediate layer, the improvement wherein said particles comprise particles of a solid, nonacid-resistant silicate which gives an alkaline reaction in aqueous suspension, said silicate being the product of heating a mixture of finely divided diatomaceous earth, a hydroxide of an alkaline earth metal, and water.

Further features of the invention will become apparent from a consideration of the following detailed description.

Theimproved corrosion resistance of the nickel/chromium coatingsobtainedfby the process according to the invention is a result of the factthatat the intermediate layer the acid medium which occurs in theelectrochemical corrosion reactions is neutralized by the silicates embedded in said intermediate layer, said silicates being nonacid-resistantand giving an alkaline reaction in water. Accordingly, in addition to the great corrosion resistance caused by the microporous nature of the chromium layer, the electrochemical corrosion reaction itself isadverselyaffected.

The silicates. to be used according to the invention, which have an alkaline reaction in water and are not acid-resistant, are conventionalfilter aids which in addition to the main component; SiO principally contain CaO and/or MgO, and generally'have aspecific gravity of from 2.0-2.8. When heated at 900C. they exhibit a considerable lossdue to calcination. A 20 percent suspension of these silicates in water has a pHof from 7.6 to 10. The silicates may be prepared in accordance with theteaching in US. Pat. No. 1,574,363, by heating a mixture of finely divided diatomaceous earth, a hydroxide of an alkaline earth metal, and water, preferably at a temperature of between and C., depending on conditions of pressure and time. The quantity of water in the mixture should be enough to contain the swollen product. Preferably the mixture contains at least 25 parts by weight of water per part by weight. of diatomaceous, earth and at least 5 percent, preferably 30-l00-percent by weight, of CaO or MgO, calculated on the weight of the diatomaceous earth.

Analyses of some of-such nonacid-resistant silicates having an alkaline reaction in water arespecified in the following table:

The average particle size of these materials is about l micron. The smallest particles are smaller than 0.1 micron.

When the alkaline reacting silicates are added to an acidic bath, for example, havinga pH of 4, the pH is increased, as

will be apparent from the following-table:

Concentration Silicate l pH 0 g./l. 4 2 g./l. 5.6 4 .11. 5.9 a J1. 61

In order that the alkaline character of the silicate be not unduly impaired, it is recommendable that the silicate is added to the bath after thepH of the latter has been adjusted to a value of at :least 6.1. for example, by means of NaOH or ammonia. The pH of the bath may also be adjusted to such a value by the addition of such. a quantity of the silicate that after the neutralization of the bath a sufficient quantity of unaffected silicate remains.

l have further found that theeffect of the nonacid-resistant silicates having an alkaline reaction in water is additionally improved when the silicate suspended in the bath from which the intermediate layer is deposited is previously impregnated with a substance which inhibite the corrosion of iron and/or nickel.

Examples of such substances are dimethyl glyoxime, which forms an insoluble compound with nickel ions formed in the corrosion of nickel, further reducing agents, such as hydrazine, which inhibit the anodic iron and/or nickel corrosion, and corrosion inhibitors, such as Shell V.P.l." (dicyclohexylamine nitrite), which gives off vapors inhibiting the corrosion of iron.

Such substances may be dissolved in a suitable medium, for example, alcohol, whereafter the nonacid-resistant silicate having an alkaline reaction in water is impregnated with such solution. After repeated washing, the product is suitable for use in the process according to the invention.

The invention is illustrated in, but not limited by, the following examples.

EXAMPLE 1 Iron covers having a surface area of 1.2 dm. were provided with a bright nickel coating by a treatment for minutes at an average current density of 5 a./dm. and utilizing cathode movement, in the following electrolytic bath:

nickel sulphate 300 g.l|, nickel chloride 60 gill. boric acid 40 g./l. quinaldine ethyl iodide 0.02 g./l. p-toluene sulfonamide 2 g.ll. sodium lauryl sulphate 0.2 g./l. pH 4.0 temperature 55 C.

After rinsing, five nickel-plated covers were respectively treated in each of the following five baths for 30 seconds at an average current density of 3 a./dm. to be provided with an intermediate layer having a thickness of 0.3 micron.

EXAMPLE ll Covers provided with a bright nickel coating in the manner described in Example I were provided with an intermediate layer having a thickness of l micron by a treatment for 1 minute, at an average current density of 5 a./dm. in the following baths:

'substantially pure diatomaceous earth (89% SiO,, 0.9% CaO+MgO After this intermediate treatment the covers were chromium plated in the manner described in Example I.

Cover F had a high brightness throughout its surface and was still without rust after six cycles in the Corrodkote test.

Cover G had a high brightness and showed 3 percent rust after four cycles in the Corrodkote test.

Cover H had a high brightness and showed 5 percent rust after four cycles in the Corrodkote test.

These results show that the nonacid-resistant silicates having an alkaline reaction in water produce a better effect for the purpose contemplated than entirely acid-resistant silicates, such as kaolin and the Cellite 505.

Bath Bath Bath Bath Bath A B C D E EXAMPLE lll Covers provided with a bright nickel coating in the manner Nickelsulvhfiie g-l 250 250 250 250 250 described in Example I were provided with an intermediate Nlcltelchloride .11. 4 4s 45 45 4O l yer having a thickness of 2.5 micron by a treatment for 2 Boric acid g./l. 30 30 30 30 30 2 5mm: L minutes, at an average current density of 2 a./dm. in the folo, (average diam. 30 lowing bright silver baths: cter 0.1 micron) g./l. ii( )=.s-/ l0 I cam" )b M. 0 Bath l Bath J Temperature,C. so so so so so 45 pH fi- 6-1 6-2 6- Silver cyanide, g./l. 40 40 "r cyanide, g./|. I20 I20 -"adjusted to pl-l=6.2 with NaOH; the bath was entirely turbid owing the gfg i sg zzr 8 m precipitated nickelhydroxide. siligael g Silicate I, washed with acid", g./l. 20 After this intermediate treatment the covers were chromi- Temperamreoc' 40 um plated for 1 minute at an average current density of 15 b h f I f I 2 a rig tener, consisting 0 an equimo ar mixture 0 se enium diethyl dithiocarbam the followmg bath mate and tetraethyl thiuram disulfide.

chmmic acid 300 gJL "thirty-five grams Silicate ll was treated with 45 cc. HCl (1:1), filtered, four times sulfuric acid 3 SIL washed with water and dried in vacuo, whereafter 20 g. solid material remained. temperature 40 C.

After this intermediate treatment the covers were chromi- Cover had a high brightness thro ighout its surface and um plated in the manner described in Example I was still without rust after five cycles in the Corrodkote test Cove, I had a high brightness and was Still without rust afler (ASTM spec'ficamm B 389/61 D' five cycles in the Corrodkote test.

Cover B had dull edges in the high current density zones and Cover J had a high brightness and showed 5 percent rust showed 3 percent rust after three cycles in the Corrodkote after three cyclesin the Corrodkote test test- These results show that the nonacid-resistant silicates hav- Cover C had lush bnghmess and Showed 3 Pennat rust 65 ing an alkaline reaction in water, to be used according to the after two cycles h cmfodkote testinvention, lose their particular effect by a treatment with acid.

Cover D had a high brightness and showed 7 percent rust after two cycles in the Corrodkote test. EXAMPLE IV Cover E had a high brightness and showed 3 percent rust v v afte'fourcydemthecmdkmetestwi ?ai'ififiniliiafiiffi i'fi'iilfiilifili1E?551K133? These results show that the nonacid-resistant silicates hav- 1 y g nonelectric baths for 3 minutes. ing an alkaline reaction in water produce an improved corrosion resistance, which is not obtained by the high pH of the Bath K Bath L solution alone, and no more by the compounds MgO and Ca() Nickel mom. ML 30 alone, which occur in these silicates in combined form. Sodium hypopholphlte, .11. i0 i0 Sodium citrate, g./l. 30 W 30 A1 0, (average diameter 50 0.l micron), g./l.

Temperature, C. 95 5 pH 6.5 6.5

without the silicate lll, the pH of the bath was 4.5

"adjusted to this value with ammonia The covers thus provided with an intermediate layer having an average thickness of about 0.5 micron were provided with a chromium coating in the manner described in Example 1.

Cover K had a high brightness and did not show a trace of corrosion after seven cycles in the Corrodkote test.

Cover L had a high brightness, but showed 5 percent rust after four cycles in the Corrodkote test.

EXAMPLE v A cover provided with a bright nickel coating in the manner described in Example I was provided with an intermediate layer of a thickness of 0.6 micron by a treatment for 1 minute in the following bath:

Bath M Nickel sulphate, g.ll. 300 Nickel chloride. g./l. 60 Boric acid, g.ll. 4S saccharine, g./l. 2 Quinaldine ethyliodide, g./|. 0.02 Silicate lV, g./l. 6.l

A plain iron cover was provided with a bright nickel coating by a treatment in the same bath M for ll minutes at an average current density of 5 a./dm.

Both covers, which had an equally thick nickel coating, were provided with a chromium coating in the manner described in Example 1.

The cover having the base nickel coating from Example I and the intermediate layer from Bath M was still free of corrosion after five cycles in the Corrodkote test, whereas the cover which had only been nickel plated in bath M, showed 5 percent of rust after four cycles in the Corrodkote test.

These results show that it is of essential importance that the nonacid-resistant silicates having an alkaline reaction in water, to be used according to the invention, are embedded in a thin intermediate layer and not in the basic nickel layer. The presence of the silicate particles in the basic nickel layer has for its result that this nickel layer becomes more brittle, which is concomitant with a decrease in the corrosion resistance.

EXAMPLE Vl Covers provided with a bright nickel coating in the manner described in Example l were provided with an intermediate layer having a thickness of 0.75 micron by a treatment for 45 seconds at an average current density of 5 a./dm. in the following baths:

Balh Bath Bath Bath N 0 P Q Nickel sulphate. g./l. 250 250 250 250 Nickel chloride, gJl. 60 60 60 60 The corrosion inhibitors (dimethyl glyoxime, hydrazine, and Shell V.P.l.) were previously applied to the silicate l by impregnation. For this purpose 10 g. of Silicate l were treated with a solution of 0.1 g. inhibitor in 10 cc. alcohol, followed by re eated washin with water and drying.

he covers t us treated were chromium plated in the manner described in Example I. All covers showed a high brightness.

Cover N showed 2-3 percent rust after nine cycles in the Corrodkote test.

Covers 0, P, and 0, however, did not show a trace of corrosion after 14 cycles in the Corrodkote test.

What I claim is:

1. In a process for coating an object with a bright nickel/chromium coating comprising the steps of providing an object having thereon a bright nickel coating, applying to said coating an intermediate metal layer containing particles from a plating bath containing said particles in suspension; and plating chromium over said intermediate layer, the improvement wherein said plating bath has a pH of at least 6.1 and wherein said particles comprise particles of a solid, nonacid-resistant silicate which in the form of a 20 percent suspension in water has a pH of at least 7.6, said silicate being the product of heating a mixture of finely divided diatomaceous earth, a hydroxide of an alkaline earth metal, and water.

2. A process according to claim 1, wherein the average diameter of said'particles does not exceed about 1 micron.

3. A process according to claim 2, wherein the concentration of said particles in said plating bath is in the range of about 2-20 grams per liter of bath.

4. A process according to claim 3, wherein said silicate is the product of heating at a temperature between C. and C. a mixture of finely divided diatomaceous earth, a hydroxide of an alkaline earth metal, and water.

5. A process according to claim 2, wherein the concentration of said particles in said plating bath is at least about 2 grams per liter of bath.

6. A process according to claim 1, wherein said particles include a corrosion inhibitor, said corrosion inhibitor being a substance which inhibits the corrosion of iron and/or nickel.

7. A process according to claim 6, wherein said corrosion inhibitor is selected from the group consisting of dimethyl glyoxime, hydrazine and dicyclohexylamine nitrite.

8. A process according to claim 1, wherein said intermediate coating is deposited electrolytically utilizing electrical current.

9. A process according to claim 1, wherein said intermediate layer is deposited by reduction without the use of an electric curre'nt.

10. A process according to claim 1, wherein the thickness of said intermediate layer does not exceed about 2.5 microns.

* i t i 

2. A process according to claim 1, wherein the average diameter of said particles does not exceed about 1 micron.
 3. A process according to claim 2, wherein the concentration of said particles in said plating bath is in the range of about 2-20 grams per liter of bath.
 4. A process according to claim 3, wherein said silicate is the product of heating at a temperature between 90* C. and 105* C. a mixture of finely divided diatomaceous earth, a hydroxide of an alkaline earth metal, and water.
 5. A process according to claim 2, wherein the concentration of said particles in said plating bath is at least about 2 grams per liter of bath.
 6. A process according to claim 1, wherein said particles include a corrosion inhibitor, said corrosion inhibitor being a substance which inhibits the corrosion of iron and/or nickel.
 7. A process according to claim 6, wherein said corrosion inhibitor is selected from the group consisting of dimethyl glyoxime, hydrazine and dicyclohexylamine nitrite.
 8. A process according to claim 1, wherein said intermediate coating is deposited electrolytically utilizing electrical current.
 9. A process according to claim 1, wherein said intermediate layer is deposited by reduction without the use of an electric current.
 10. A process according to claim 1, wherein the thickness of said intermediate layer does not exceed about 2.5 microns. 